1. Field of the Invention
With the loss of suitable habitat for cavity nesting birds there has developed a competition for remaining tree cavities and artificially provided nest boxes. This invention relates to a device which prevents prolific birds (such as the European Starling) from procuring nest sites from rarer avian species. The apparatus constitutes a shield that is placed over the entrance hole that allows access to only those birds capable of scaling a vertical surface (such as woodpeckers).
2. Description of the Prior Art
While attention has been devoted to restricting the access to avian cavity nests at the entrance site the selective factor has focused on the size of the entrance hole.
The prior disclosure of Larson (U.S. Pat. No. 1,209,979) demonstrates a truncated cone structure with the smaller end serving as the entrance opening. The only discriminating factor in this presentation is the diameter of the entrance hole specifically governing passage of bird species of different sizes. It does not distinguish between birds that may be the same size.
Besherer (U.S. Pat. No. 4,318,364) presents curved shaped channels that approximate the size of the bird. However, these protective channels are designed and utilized to merely act as access ports to a feeder in which the bird obtains seeds that lie at its lower end. The function of structure 28 of Bescherer is to serve as a buffer to prevent seed from spilling out of a bird feeder while providing birds with a location with which to acquire the seed. It does not function as a restrictive device and allows birds of varying sizes access to the seed so long as their beaks may negotiate the porthole. The configuration of the port channel is arranged for easy access from above such that any bird may gain access by simply lowering its head. The need exists for a configuration whereby the bird is challenged to enter an access opening from below to gain access to a nesting cavity.
The prior patent disclosure of Parker (U.S. Pat. No. 5,228,410) calls for a "safe entry for bird houses". Again, this patent concerns itself with entry restrictions simply in terms of the size of the bird. It selects for smaller birds. And it allows for entry of any bird that can fly to and grasp a protruding perch-like structure. But what happens when you are trying to discriminate between two birds that are the same size?